Methods and Arrangements for CSI Reporting

ABSTRACT

A method in a wireless device for reporting Channel State Information (CSI). The wireless device is comprised in a wireless communications system. The method includes receiving a CSI process configuration and a request for CSI information from a network node. The method further includes reporting CSI for one or more CSI processes. The CSI reflects the state of the channel for a CSI reference resource. According to the method, the CSI reference resource is determined based on the number of configured CSI processes. Related devices are also disclosed.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is responsible for thestandardization of the Universal Mobile Telecommunication System (UMTS)and Long Term Evolution (LTE). The 3GPP work on LTE is also referred toas Evolved Universal Terrestrial Access Network (E-UTRAN). LTE is atechnology for realizing high-speed packet-based communication that canreach high data rates both in the downlink and in the uplink, and isthought of as a next generation mobile communication system relative toUMTS. In order to support high data rates, LTE allows for a systembandwidth of 20 MHz, or up to 100 Hz when carrier aggregation isemployed. LTE is also able to operate in different frequency bands andcan operate in at least Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) modes.

LTE uses orthogonal frequency-division multiplexing (OFDM) in thedownlink and discrete-Fourier-transform-spread (DFT-spread) OFDM in theuplink. The basic LTE physical resource can be seen as a time-frequencygrid, as illustrated in FIG. 1, where each time-frequency resourceelement (TFRE) corresponds to one subcarrier during one OFDM symbolinterval, on a particular antenna port. There is one resource grid perantenna port. The resource allocation in LTE is described in terms ofresource blocks, where a resource block corresponds to one slot in thetime domain and 12 contiguous 15 kHz subcarriers in the frequencydomain. Two time-consecutive resource blocks represent a resource blockpair, which corresponds to the time interval upon which schedulingoperates.

An antenna port is a “virtual” antenna, which is defined by an antennaport-specific reference signal (RS). An antenna port is defined suchthat the channel over which a symbol on the antenna port is conveyed canbe inferred from the channel over which another symbol on the sameantenna port is conveyed. The signal corresponding to an antenna portmay possibly be transmitted by several physical antennas, which may alsobe geographically distributed. In other words, an antenna port may betransmitted from one or several transmission points. Conversely, onetransmission point may transmit one or several antenna ports. Antennaports may interchangeably be referred to as “RS ports”.

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance is inparticular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO.

The LTE standard is currently evolving with enhanced MIMO support. Acore component in LTE is the support of MIMO antenna deployments andMIMO related techniques. LTE Release 10 and above (also referred to asLTE-Advanced) enables support of eight-layer spatial multiplexing withpossibly channel dependent precoding. Such spatial multiplexing is aimedfor high data rates in favorable channel conditions. An illustration ofprecoded spatial multiplexing is provided in FIG. 2.

As seen, the information carrying symbol vector s is multiplied by anN_(T)×r precoder matrix W_(N) _(T) _(×r), which serves to distribute thetransmit energy in a subspace of the N_(T) dimensional vector space,where N_(T) corresponds to the number of antenna ports. The r symbols ins each are part of a symbol stream, a so-called layer, and r is referredto as the transmission rank. In this way, spatial multiplexing isachieved since multiple symbols can be transmitted simultaneously overthe same TFRE. The number of layers, r, is typically adapted to suit thecurrent channel properties.

Furthermore, the precoder matrix is often selected from a codebook ofpossible precoder matrices, and typically indicated by means of aprecoder matrix indicator (PMI), which for a given rank specifies aunique precoder matrix in the codebook. If the precoder matrix isconfined to have orthonormal columns, then the design of the codebook ofprecoder matrices corresponds to a Grassmannian subspace packingproblem.

The received N_(R)×1 vector y_(n) on the data TFRE indexed n is modeledby

y _(n) =H _(n) W _(N) _(T) _(×r) S _(n) +e _(n)  (1)

where e_(n) is a noise plus interference vector modeled as realizationsof a random process. The precoder for rank r, W_(N) _(T) _(×r), can be awideband precoder, which is either constant over frequency, or frequencyselective.

The precoder matrix is often chosen to match the characteristics of theN_(R)×N_(T) MIMO channel H, resulting in so-called channel dependentprecoding. When based on UE feedback, this is commonly referred to asclosed-loop precoding and essentially strives for focusing the transmitenergy into a subspace which is strong in the sense of conveying much ofthe transmitted energy to the UE. In addition, the precoder matrix mayalso be selected to strive for orthogonalizing the channel, meaning thatafter proper linear equalization at the UE, the inter-layer interferenceis reduced.

In closed-loop precoding, the UE transmits, based on channelmeasurements in the forward link, or downlink, recommendations to thebase station, which in LTE is called the evolved NodeB (eNodeB) of asuitable precoder to use. A single precoder that is supposed to cover alarge bandwidth (wideband precoding) may be fed back. It may also bebeneficial to match the frequency variations of the channel and insteadfeed back a frequency-selective precoding report, e.g. severalprecoders, one per subband. This is an example of the more general caseof channel state information (CSI) feedback, which also encompassesfeeding back other entities than precoders to assist the eNodeB insubsequent transmissions to the UE. Thus, channel state information mayinclude one or more of PMI, channel quality indicators (CQIs) or rankindicator (RI).

Signal and channel quality estimation is a fundamental part of a modernwireless system. Noise and interference estimates are used not only inthe demodulator, but are also important quantities when estimating, forexample, the channel quality indicator (CQI), which is typically usedfor link adaptation and scheduling decisions on the eNodeB side.

The term e_(n) in (1) represents noise and interference in a TFRE and istypically characterized in terms of second order statistics such asvariance and correlation. The interference can be estimated in severalways including from the cell-specific reference symbols (RS) that arepresent in the time-frequency grid of LTE. Such RS may correspond to theRel-8 cell-specific RS, CRS (antenna ports 0-3), which are illustratedin FIG. 3, as well as the new CSI RS available in Rel-10, which will bedescribed in more detail below. CRS are sometimes also referred to ascommon reference signals.

Estimates of interference and noise can be formed in various ways.Estimates can easily be formed based on TFREs containing cell specificRS since s_(n) and W_(N) _(T) _(×r) are then known and H_(n) is given bythe channel estimator. It is further noted that the interference onTFREs with data that is scheduled for the UE in question can also beestimated as soon as the data symbols, s_(n) are detected, since at thatmoment they can be regarded as known symbols. The latter interferencecan alternatively also be estimated based on second order statistics ofthe received signal and the signal intended for the UE of interest, thuspossibly avoiding needing to decode the transmission before estimatingthe interference term. Alternatively the interference can be measured onTFREs where the desired signal is muted, so the received signalcorresponds to interference only. This has the advantage that theinterference measurement may be more accurate and the UE processingbecomes trivial because no decoding or desired signal subtraction needto be performed.

Channel State Information Reference Signal (CSI-RS)

In LTE Release-10, a new reference symbol sequence, the CSI-RS, wasintroduced for the purpose of estimating channel state information. TheCSI-RS provides several advantages over basing the CSI feedback on thecell-specific reference symbols (CRS) which were used for that purposein previous releases. Firstly, the CSI-RS is not used for demodulationof the data signal, and thus does not require the same density. In otherwords, the overhead of the CSI-RS is substantially less. Secondly,CSI-RS provides a much more flexible means to configure CSI feedbackmeasurements. For example, which CSI-RS resource to measure on can beconfigured in a UE specific manner. Moreover, the support of antennaconfigurations larger than 4 antennas must resort to CSI-RS, since theCRS is only defined for at most 4 antennas.

By measuring on a CSI-RS a UE can estimate the effective channel theCSI-RS is traversing including the radio propagation channel, antennagains, and any possible antenna virtualizations. A CSI-RS port may beprecoded so that it is virtualized over multiple physical antenna ports;that is, the CSI-RS port can be transmitted on multiple physical antennaports, possibly with different gains and phases. In more mathematicalrigor this implies that if a known CSI-RS signal x_(n) is transmitted, aUE can estimate the coupling between the transmitted signal and thereceived signal, i.e. the effective channel. Hence if no virtualizationis performed in the transmission:

y _(n) =H _(n) x _(n) +e _(n)

the UE can measure the effective channel H_(eff)=H_(n). Similarly, ifthe CSI-RS is virtualized using a precoder W_(N) _(T) _(×r) as

y _(n) =H _(n) W _(N) _(T) _(×r) x _(n) +e _(n)

the UE can estimate the effective channel H_(eff)=H_(n)W_(N) _(T) _(×r).

Related to CSI-RS is the concept of zero-power CSI-RS resources (alsoknown as a muted CSI-RS) that are configured just as regular CSI-RSresources, so that a UE knows that the data transmission is mappedaround those resources. The intent of the zero-power CSI-RS resources isto enable the network to mute the transmission on the correspondingresources as to boost the SINR of a corresponding non-zero power CSI-RS,possibly transmitted in a neighbor cell/transmission point. For Rel-11of LTE, a special zero-power CSI-RS that a UE is mandated to use formeasuring interference plus noise is under discussion. As the nameindicates, a UE can assume that the TPs of interest are not transmittingon the muted CSI-RS resource and the received power can therefore beused as a measure of the interference plus noise level.

Based on a specified CSI-RS resource and an interference measurementconfiguration, e.g. a muted CSI-RS resource, the UE can estimate theeffective channel and noise plus interference, and consequently alsodetermine which rank, precoder and transport format to recommend thatbest match the particular channel.

Coordinated Multipoint Transmission (CoMP)

CoMP transmission and reception refers to a system where thetransmission and/or reception at multiple, geographically separatedantenna sites is coordinated in order to improve system performance.More specifically, CoMP refers to coordination of antenna arrays thathave different geographical coverage areas. In the subsequent discussionwe refer to a set of antennas covering essentially the same geographicalarea in the same manner as a point, or more specifically as aTransmission Point (TP). Thus, a point might correspond to one of thesectors at a site, but it may also correspond to a site having one ormore antennas all intending to cover a similar geographical area. Often,different points represent different sites. Antennas correspond todifferent points when they are sufficiently geographically separatedand/or have antenna diagrams pointing in sufficiently differentdirections. Although the present disclosure focuses mainly on downlinkCoMP transmission, it should be appreciated that in general, atransmission point may also function as a reception point. Thecoordination between points can either be distributed, by means ofdirect communication between the different sites, or by means of acentral coordinating node. A set of points that perform coordinatedtransmission and/or transmission is referred to as a CoMP coordinationcluster, a coordination cluster, or simply as a cluster in thefollowing.

FIG. 5 shows an example wireless network with a CoMP coordinationcluster comprising three transmission points, denoted TP1, TP2 and TP3.

CoMP is a tool introduced in LTE to improve the coverage of high datarates, the cell-edge throughput and/or to increase system throughput. Inparticular, the goal is to distribute the user perceived performancemore evenly in the network by taking control of the interference in thesystem, either by reducing the interference and/or by better predictionof the interference.

CoMP operation targets many different deployments, includingcoordination between sites and sectors in cellular macro deployments, aswell as different configurations of Heterogeneous deployments, where forinstance a macro node coordinates the transmission with pico nodeswithin the macro coverage area.

There are many different CoMP transmission schemes that are considered;for example,

Dynamic Point Blanking where multiple transmission points coordinatesthe transmission so that neighboring transmission points may mute thetransmissions on the time-frequency resources (TFREs) that are allocatedto UEs that experience significant interference.

Coordinated Beam forming where the TPs coordinate the transmissions inthe spatial domain by beamforming the transmission power in such a waythat the interference to UEs served by neighboring TPs are suppressed.

Dynamic Point Selection where the data transmission to a UE may switchdynamically (in time and frequency) between different transmissionpoints, so that the transmission points are fully utilized.

Joint Transmission where the signal to a UE is simultaneouslytransmitted from multiple TPs on the same time/frequency resource. Theaim of joint transmission is to increase the received signal powerand/or reduce the received interference, if the cooperating TPsotherwise would serve some other UEs without taking our JT UE intoconsideration.

CoMP Feedback

A common denominator for the CoMP transmission schemes is that thenetwork needs CSI information not only for the serving TP, but also forthe channels linking the neighboring TPs to a terminal. By, for example,configuring a unique CSI-RS resource per TP, a UE can resolve theeffective channels for each TP by measurements on the correspondingCSI-RS. Note that the UE is likely unaware of the physical presence of aparticular TP, it is only configured to measure on a particular CSI-RSresource, without knowing of any association between the CSI-RS resourceand a TP.

A detailed example showing which resource elements within a resourceblock pair may potentially be occupied by UE-specific RS and CSI-RS isprovided in FIG. 4. In this example, the CSI-RS utilizes an orthogonalcover code of length two to overlay two antenna ports on two consecutiveREs. As seen, many different CSI-RS patterns are available. For the caseof 2 CSI-RS antenna ports, for example, there are 20 different patternswithin a subframe. The corresponding number of patterns is 10 and 5 for4 and 8 CSI-RS antenna ports, respectively.

A CSI-RS resource may be described as the pattern of resource elementson which a particular CSI-RS configuration is transmitted. One way ofdetermining a CSI-RS resource is by a combination of the parameters“resourceConfig”, “subframeConfig”, and “antennaPortsCount”, which maybe configured by RRC signaling.

Several different types of CoMP feedback are possible. Most alternativesare based on per CSI-RS resource feedback, possibly with CQI aggregationof multiple CSI-RS resources, and also possibly with some sort ofco-phasing information between CSI-RS resources. The following is anon-exhaustive list of relevant alternatives (note that a combination ofany of these alternatives is also possible):

Per CSI-RS resource feedback corresponds to separate reporting ofchannel state information (CSI) for each of a set of CSI-RS resources.Such a CSI report may, for example, comprise one or more of a PrecoderMatrix Indicator (PMI), Rank Indicator (RI), and/or Channel QualityIndicator (CQI), which represent a recommended configuration for ahypothetical downlink transmission over the same antennas used for theassociated CSI-RS, or the RS used for the channel measurement. Moregenerally, the recommended transmission should be mapped to physicalantennas in the same way as the reference symbols used for the CSIchannel measurement.

Typically there is a one-to-one mapping between a CSI-RS and a TP, inwhich case per CSI-RS resource feedback corresponds to per-TP feedback;that is, a separate PMI/RI/CQI is reported for each TP. Note that therecould be interdependencies between the CSI reports; for example, theycould be constrained to have the same RI. Interdependencies between CSIreports have many advantages, such as; reduced search space when the UEcomputes feedback, reduced feedback overhead, and in the case of reuseof RI there is a reduced need to perform rank override at the eNodeB.

The considered CSI-RS resources are configured by the eNodeB as the CoMPMeasurement Set. In the example shown in FIG. 5, different measurementsets may be configured for wireless devices 540 and 550. For example,the measurement set for wireless device 540 may consist of CSI-RSresources transmitted by TP1 and TP2, since these points may be suitablefor transmission to device 540. The measurement set for wireless device550 may instead be configured to consist of CSI-RS resources transmittedby TP2 and TP3. The wireless devices will report CSI information for thetransmission points corresponding to their respective measurement sets,thereby enabling the network to e.g. select the most appropriatetransmission point for each device.

Aggregate feedback corresponds to a CSI report for a channel thatcorresponds to an aggregation of multiple CSI-RS. For example, a jointPMI/RI/CQI can be recommended for a joint transmission over all antennasassociated with the multiple CSI-RS.

A joint search may however be too computationally demanding for the UE,and a simplified form of aggregation is to evaluate an aggregate CQIwhich are combined with per CSI-RS resource PMIs, which should typicallyall be of the same rank corresponding to the aggregated CQI or CQIs.Such a scheme also has the advantage that the aggregated feedback mayshare much information with a per CSI-RS resource feedback. This isbeneficial, because many CoMP transmission schemes require per CSI-RSresource feedback, and to enable eNodeB flexibility in dynamicallyselecting CoMP scheme, aggregated feedback would typically betransmitted in parallel with per CSI-RS resource feedback. To supportcoherent joint transmission, such per CSI-RS resource PMIs can beaugmented with co-phasing information enabling the eNodeB to rotate theper CSI-RS resource PMIs so that the signals coherently combine at thereceiver.

Interference Measurements for CoMP

For efficient CoMP operation it is equally important to captureappropriate interference assumptions when determining the CSI as it isto capture the appropriate received desired signal.

For the purpose of this disclosure, a CSI process is defined as thereporting process of CSI (e.g., CQI and potentially associated PMI/RI)for a particular effective channel, and an interference measurementresource. Optionally, a CSI process may also be associated with one ormore interference emulation configurations, as will be explained below.The effective channel is defined by a reference signal resourcecomprising one or multiple associated reference sequences. Theinterference measurement resource is a set of resource elements in whichone or more signals that are assumed to be interfering with the desiredsignal are received. The IMR may correspond to a particular CQIreference resource, e.g. a CRS resource. Alternatively, the IMR may be aresource configured specifically for measuring interference.

In uncoordinated systems the UE can effectively measure the interferenceobserved from all other TPs (or all other cells), which will be therelevant interference level in an upcoming data transmission. Suchinterference measurements are typically performed by analyzing theresidual interference on CRS resources, after the UE subtracts theimpact of the CRS signal. In coordinated systems performing CoMP suchinterference measurements becomes increasingly irrelevant. Most notably,within a coordination cluster an eNodeB can to a large extent controlwhich TPs that interfere a UE in any particular TFRE. Hence, there willbe multiple interference hypotheses depending on which TPs aretransmitting data to other terminals.

For the purpose of improved interference measurements new functionalityis introduced in LTE Release 11, where the agreement is that the networkwill be able to configure which particular TFREs that is to be used forinterference measurements for a particular UE; this is defined as aninterference measurement resource (IMR). The network can thus controlthe interference seen on a IMR, by for example muting all TPs within acoordination cluster on the associated TFREs, in which case the terminalwill effectively measure the inter CoMP cluster interference. In theexample shown in FIG. 5, this would correspond to muting TP1, TP2 andTP3 in the TFREs associated with the IMR.

Consider for example a dynamic point blanking scheme, where there are atleast two relevant interference hypotheses for a particular UE: in oneinterference hypothesis the UE sees no interference from the coordinatedtransmission point; and in the other hypothesis the UE sees interferencefrom the neighboring point. To enable the network to effectivelydetermine whether or not a TP should be muted, the network may configurethe UE to report two, or generally multiple CSIs corresponding todifferent interference Hypotheses—that is, there can be two CSIprocesses corresponding to different interference situations. Continuingthe example of FIG. 5, assume that the wireless device 550 is configuredto measure CSI from TP3. However, TP2 may potentially interfere with atransmission from TP2, depending on how the network schedules thetransmission. Thus, the network may configure the device 550 with twoCSI processes for TP3 (or, more specifically, for measuring the CSI-RStransmitted by TP3). One CSI process is associated with the interferencehypothesis that TP2 is silent, and the other CSI process corresponds tothe hypothesis that TP3 is transmitting an interfering signal.

To facilitate such a scheme it has been proposed to configure multipleIMRs, wherein the network is responsible for realizing each relevantinterference hypothesis in the corresponding IMR. Hence, by associatinga particular IMR with a particular CSI process, relevant CSIinformation, e.g. CQI, can be made available to the network foreffective scheduling. In the example of FIG. 5, the network may, forexample, configure one IMR in which only TP2 is transmitting, andanother IMR in which TP2 and TP3 are both silent. Each CSI process maythen be associated with a different IMR.

Another approach for estimating interference, which may be used inconjunction with measurements based on an IMR, is to have the terminalemulate interference from within the coordinated points according to aninterference hypothesis, by for example assuming an isotropictransmission from each of the transmission points that are assumedinterfering for the interference hypothesis. This has the advantage thatit may be sufficient that the terminal performs interferencemeasurements on a single IMR, where there is no interference from thecoordinated transmission points, from which each of the interferencehypothesis are derived. For example, assume that this residualinterference and noise is measured and characterized, by the terminal,as a complex valued Gaussian random process

e_(n)∈CN(0,Q_(e)),

where Q_(e) is the correlation matrix and the elements of e_(n)corresponds to an interference realization on each of the receiveantennas. Then the terminal can amend the residual interference tocorrespond to a particular CoMP interference hypothesis by emulatingintra CoMP cluster interference from a transmission point, for which ithas measured an effective channel, H_(eff), as

{tilde over (e)} _(n) =e _(n) +H _(eff) q _(n)

where q_(n) is an isotropic random signal of a specific nominal power.Note, however, that for a terminal to be able to emulate intra CoMPcluster interference the terminal needs to acquire a reliable channelestimate for each point it should add interference for, which means thatthe associated reference signals need to be known and have asufficiently high SINR.

If interference emulation is applied, a CSI process may furthercorrespond to one or more interference emulation configurations. Eachinterference emulation configuration is associated with a referencesignal received from an assumed interferer. The wireless deviceestimates, for each interference emulation configuration, an effectivechannel based on the associated reference signal. The wireless devicethen emulates interference for each interference emulation configurationbased on the estimated effective channel for that configuration. Asexplained above, one way of emulating interference is to multiply thechannel estimate by an isotropic random signal.

Although the possibility of associating a CSI process with one or moreIMRs and/or interference emulation configurations enables the network toobtain a better basis for making link adaptation and schedulingdecisions, there is still room for further improvement when determiningchannel state information.

SUMMARY

An object of the present invention is to provide an improved mechanismfor determining channel state information.

Some embodiments disclosed herein provide a method in a wireless devicefor reporting Channel State Information, CSI. The wireless device iscomprised in a wireless communications system 500. The method comprisesreceiving a CSI process configuration and a request for CSI informationfrom a network node. Further, the wireless device reports CSI for one ormore CSI processes, wherein the CSI is determined such as to reflect thestate of the channel for a CSI reference resource. According to themethod, the CSI reference resource is determined based on the number ofconfigured CSI processes.

Some embodiments provide a wireless device for reporting CSI. Thewireless device is adapted to receive a CSI process configuration and arequest for CSI information from a network node. The wireless device isfurther adapted to report CSI for one or more CSI processes, wherein theCSI is determined such as to reflect the state of the channel for a CSIreference resource. Furthermore, the CSI reference resource isdetermined based on the number of configured CSI processes.

Yet further embodiments provide a user equipment for reporting CSI. Theuser equipment comprises a processor and a memory. The memory comprisesinstructions which, when executed, cause the user equipment to beconfigured to receive a CSI process configuration and a request for CSIinformation from a network node, and further cause the user equipment tobe configured to report CSI for one or more CSI processes, wherein theCSI is determined such as to reflect the state of the channel for a CSIreference resource, and wherein the CSI reference resource is determinedbased on the number of configured CSI processes.

An advantage of some embodiments disclosed herein is that the requiredpeak processing capability of a wireless device can be reduced, whilemaintaining acceptable support also for large CoMP feedbackconfigurations. This is made possible in some embodiments by making thelocation of the CSI reference resource dependent on some parameter(s),e.g. the number of configured CSI processes, thereby effectivelyincreasing the CSI processing time window for the wireless device whenthis is likely to be needed.

DETAILED DESCRIPTION

A typical processing in a UE involved for determining a CSI report for aspecific CSI process can be divided as:

1) Receiving at least one reference signal that defines a desiredeffective channel for said specific CSI process.

2) Receiving interference and noise on a specific interferencemeasurement resource (IMR) associated with said specific CSI process.

3) Estimating/determining a desired effective channel from said receivedat least one reference signal.

4) Estimating a received interference and noise covariance, or level,from said received interference and noise

5) Assessing the performance of each transmission rank and precoder in acodebook

6) Selecting the PMI and RI corresponding to the highest performance(typically the PMI and RI combination that results in the highestthroughput without exceeding a target BLER or 10%)

7) Determining a CQI (or multiple in case of rank >1) for the selectedPMI/RI, involving selecting the highest CQI (recommended transport blocksize) that does not exceed a target BLER of 10%.

Each of these steps involves a non-negligible processing load in atypical UE implementation. In particular steps 5) to 7) above involvessubstantial processing. Moreover, these demanding steps cannot beperformed prior to steps 1) through 4).

The UE is required to process CSI within a certain time frame afterreceiving a specific reference signal, or performing a specificinterference measurement. This requirement may be encoded into astandard, e.g. the standard may mandate that the UE must be capable toreport CSI a certain number of subframes (e.g. 4 subframes) after thesubframe wherein the corresponding CSI-RS is transmitted. It should benoted that according to the prior art, this timing requirement is staticand the same timing requirement applies to all UE:s and all CSI reports.For example, in 3GPP LTE the processing time frame is determined by theso-called CSI reference resource with occurs 4 subframes prior to thetime frame in which the CSI report is transmitted (or the first validdownlink subframe prior to this instance). Strictly speaking the CSIreference resource specifies, or is defined by<, a specific subframe forwhich the CSI report should accurately reflect the state of the channel;this implies that the UE should base the CSI report on the referencesignals and interference and noise received within this subframe andprior to this subframe. See also FIG. 8 a.

In a scenario where the UE is configured with multiple CSI processes, itis possible that some or all of the corresponding reference signalresources and IMRs occur in the same subframe, in which case it maybecome difficult for the UE to determine all the required CSIinformation within the specified time frame.

From a UE processing budget perspective, the worst case scenario is thatall IMRs and all reference signals associated with a plurality of CSIprocesses all occur in a single subframe, because then all CSI processesmust be computed simultaneously. Such a scenario could occur e.g. if allzero-power CSI-RS configured for a UE would share the same subframeoffset and periodicity configuration, since this would imply that mutingcould only be configured for a single subframe within a period. Sincethe transmission of a CSI-RS should typically be matched by acorresponding muting in neighboring transmission points (to boost theSINR on the received CSI-RS signals), the transmission of a CSI-RS wouldin practice be confined to the same subframe as the mutingconfigurations. Hence, it is quite possible that the worst-case scenariocould occur in practice.

Such a situation is illustrated in FIG. 6, where the UE is required tofinalize the CSI processing during a predetermined processing time afterthe reception (step 1 and 2 above), so that reporting after theprocessing time will contain updated reports. Designing a UE to managethis worst case scenario may lead to very high implementation cost. Thisproblem becomes particularly severe if large CoMP Measurement Set sizesare supported in the standard, and/or if a large number of parallel CSIprocesses are supported by the standard.

Thus, a possible solution to the problems described above would be tolimit the size of the CoMP measurement set and/or the number of parallelCSI processes. This would reduce the processing requirements on the UE,but on the other hand means that the potential benefits of CoMP cannotbe fully exploited.

A basic concept of some embodiments is therefore to reduce the peakprocessing requirement of a wireless device for CSI reporting byintroducing a processing time window, also referred to as a maximum CSIprocessing time, which may either device-specific orCSI-process-specific. The maximum processing time may be expressed e.g.in subframes or milliseconds. The length of the time window may e.g. bedependent on the total number of CSI processes, or the number of CSI-RSresources, configured for the wireless device. For example, a CSIreference resource may depend on the number of configured CSI-RSresources or number of CSI processes.

FIG. 5 illustrates an example wireless communications system 500 inwhich various embodiments of the invention may be implemented. The threetransmission points 510, 520 and 530 form a CoMP coordination cluster.In the following, for purposes of illustration and not limitation, itwill be assumed that the communications system 500 is an LTE system.Transmission points 510, 520 and 530 are remote radio units (RRU:s),controlled by eNodeB 560. In an alternative scenario (not shown), thetransmission points could be controlled by separate eNodeBs. It shouldbe appreciated that, generally speaking, each network node, e.g. eNodeB,may control one or more transmission points, which may either bephysically co-located with the network node, or geographicallydistributed. In the scenario shown in FIG. 5, it is assumed that thetransmission points 510, 520 and 530 are connected to eNodeB 560, e.g.by optical cable or a point-to-point microwave connection. In the casewhere some or all of the transmission point forming the cluster arecontrolled by different eNodeBs, those eNodeBs would be assumed to beconnected with each other e.g. by means of a transport network, to beable to exchange information for possible coordination of transmissionand reception.

It should be appreciated that although examples herein refer to aneNodeB for purposes of illustration, the invention applies to anynetwork node. The expression “network node” as used in this disclosureis intended to encompass any radio base station, e.g. an eNodeB, NodeB,Home eNodeB or Home NodeB, or any other type of network node thatcontrols all or part of a CoMP cluster.

The communications system 500 further comprises two wireless devices 540and 550. Within the context of this disclosure, the term “wirelessdevice” encompasses any type of wireless node which is able tocommunicate with a network node, such as a base station, or with anotherwireless device by transmitting and/or receiving wireless signals. Thus,the term “wireless device” encompasses, but is not limited to: a userequipment, a mobile terminal, a stationary or mobile wireless device formachine-to-machine communication, an integrated or embedded wirelesscard, an externally plugged in wireless card, a dongle etc. The wirelessdevice may also be a network node, e.g. a base station. Throughout thisdisclosure, whenever the term “user equipment” is used this should notbe construed as limiting, but should be understood as encompassing anywireless device as defined above.

In some embodiments (see FIG. 8 c), a wireless device reports CSI for aCSI process.

The wireless device receives CSI process configuration, and a CSIrequest, from a network node.

The wireless device performs measurements on CSI-RS resources andinterference measurement resources corresponding to the configured CSIprocesses. When a measurement is performed in a certain subframe, thewireless device will begin processing the received information for thepurpose of determining channel state information for the correspondingCSI process. However, as mentioned above, this processing will take acertain amount of time to complete. It should be noted that a particularinterference measurement resource may be shared by multiple CSIprocesses, in which case the interference measurement only has to beperformed once in a particular subframe.

Similarly, the desired signal reference signal resource may be shared bymultiple CSI processes, in which case the associated channel estimationonly need to be performed once in a particular subframe.

The wireless device subsequently reports CSI for one or more processes,wherein the CSI is determined based on measurements performed in and/oror prior to a CSI reference resource. The wireless device determines theCSI reference resource depending on one or more of: the number ofconfigured CSI-RS resources, the number of configured CSI processes, orthe number of configured CSI-RS resources that occur in the samesubframe.

For instance, the wireless device may determine a number n_(CQI) _(—)_(ref) based on the number of configured CSI-RS resources, and/or basedon the number of configured CSI processes, where n_(CQI) _(—) _(ref)represents the location of the CSI reference resource relative to thesubframe in which the CSI report is transmitted (as shown in FIG. 8 a).In a particular example, n_(CQI) _(—) _(ref) increases with the numberof configured CSI processes. Stated differently, if the number ofconfigured CSI processes increases, n_(CQI) _(—) _(ref) also increases.

As a specific example, if the number of configured CSI-RS (or number ofconfigured CSI processes) exceeds 2, n_(CQI) _(—) _(ref) is set to 5,whereas otherwise, n_(CQI) _(—) _(ref) is set to 4. This accounts forthe additional processing time that is required in the wireless devicefor the larger number of CSI-RS (or CSI processes). Stated differently,if the number of configured CSI-RS (or number of configured CSIprocesses) exceeds 2, the CSI reference resource is determined to be 5subframes prior to the subframe when CSI is reported, and otherwise, theCSI reference resource is determined to be 4 subframes prior to thesubframe when CSI is reported.

In one variant, the CSI reference resource is specific to the wirelessdevice. For example, the wireless device determines one number n_(CQI)_(—) _(ref) which is applied to all CSI processes configured for thedevice.

In some embodiments, the CSI reference resource is CSI-process-specific,see FIG. 8 d. For example, the wireless device obtains or determines adifferent value n_(CQI) _(—) _(ref) for each CSI process, as exemplifiedin FIG. 8 b.

In a particular variant, the wireless device receives informationindicating the CSI reference resource for each CSI process from anetwork node. As a specific example, the wireless device receives avalue n_(CQI) _(—) _(ref) for each CSI process from a network node, e.g.as part of downlink control information, or comprised in CSI processconfiguration information, or in a separate message, such as an RRCmessage. This allows the network node to prioritize between differentCSI processes, or, stated differently, to control which CSI processesare processed first.

Another possibility is that the wireless device receives or determines apriority indication for each CSI process. As will be described below,the priority indication may be determined based on a causality betweendifferent CSI processes. For example, two CSI processes may be relatedsuch that the rank of the first CSI process can be reused for the secondCSI process, in which case the first CSI process would have a higherpriority (indicating that it should be processed before the secondprocess). The CSI reference resource for each CSI process is thendetermined based on the priority.

FIGS. 8 e-8 f show corresponding embodiments in a network node.

The methods illustrated in FIGS. 8 c-8 f may be implemented in thenetwork shown in FIG. 5.

Some embodiments provide a processing time window for a specific CSIreport of a CSI process, wherein the length of the processing timewindow increases when the CSI reporting configuration corresponds to acomputational complexity heavy configuration. For example, theprocessing time window may increase with an increased number ofconfigured CSI processes and/or configured CSI-RSs. The processing timewindow may also be referred to as a “maximum CSI processing time” or“allowed CSI processing time”.

Alternatively, the processing time window of a CSI report of a specificCSI process increases with the number of CSI reports that are associatedwith a higher priority than the specific CSI process.

The UE can then not be expected to update a CSI report based on newmeasurements, prior to said time window has passed after thecorresponding measurement.

One embodiment of the invention is illustrated in FIG. 7. Here the totalprocessing time, before a complete CSI report based on the measurementscan be expected from the terminal, is extended. The duration of theextended processing time relates to the expected computationalcomplexity of determining the CSI report(s) for the CSI processes. Forexample, it is a function of the number of configured CSI processesand/or the number of CSI-RSs configured. The extended processing timecould, for example be standardized and determined from a look up tablefrom known parameters.

In another embodiment, a specific processing time window can bedetermined for a specific CSI process, so that a CSI report for said CSIprocess triggered after said specific processing time window is updatedwith the new measurements.

Such an embodiment is illustrated in FIG. 8, where the processing timewindow of CSI Process 1 is one subframe, the processing time window ofCSI Process 2 is 2 subframes, and the processing time window of CSIProcess 3 is 3 subframes. Hence, after 2 subframes a CSI report can onlybe expected to contain updated information for CSI Processes 1 and 2,whereas any information relating to CSI Process 3 cannot be expected toaccount for the new measurements. Only reports triggered after at least3 subframes can be expected to be updated with new measurements for allCSI Processes.

In one embodiment a minimum processing capability of the terminal ismandated by the standard, in terms of the number of CSI Processes thatit should be capable of determining in a specified timeframe. Forexample, it could be mandated that the terminal should be able toprocesses N CSI Processes in M subframes. For example, it could bemandated that a terminal shall be capable of determining a report fortwo CSI Processes in each subframe.

In a further embodiment, the UE is capable of processing more than themandated minimums number of CSI Processes in a given subframe.

In one embodiment there is a prioritization between multiple CSIProcesses identifying in which order the UE is expected to processesmultiple configured CSI Processes.

In one embodiment the reporting prioritization is configurable by thenetwork. In one such embodiment, each CSI Process is assigned a priorityindicator that determines in which order the CSI Processes should becomputed.

It should be noted that a particular interference measurement resourcemay be shared by multiple CSI processes, in which case the interferencemeasurement only has to be performed once.

Similarly, the desired signal reference signal resource may be shared bymultiple CSI processes, in which case the associated channel estimationonly need to be performed once.

Also, a RI and/or a PMI, may be determined as part of a first CSIprocess (assuming the associated desired effective channel andinterference measurement) and reused also in a second CSI process. Inthis case, the PMI and RI do not involve any processing in thedetermining of the second CSI process. However, the CQI of the secondCSI process should be determined using the interference measurements,and desired signal reference signals, of the second CSI process.

In one such embodiment, the prioritization is such that said first CSIprocess is prioritized over, implying that it should be processed priorto, said second CSI process. In a further embodiment, it is mandated bythe standard that the first CSI process is prioritized over the secondCSI process.

This has the advantage that UE may exploit that the reporting of the CSIprocesses is aligned with the causality of the dependencies of the CSIprocesses; that is, for the processing of the second CSI processes, theassumed the RI and/or PMI are available, since they were alreadydetermined as part of the reporting for the first CSI process.

An advantage of some embodiments is that the required peak processingcapability of a UE can be reduced, while maintaining acceptable supportalso for large CoMP feedback configurations.

FIG. 9 is a combined signaling diagram and flowchart illustrating theinteraction between a network node and a wireless device in someembodiments.

FIGS. 10-12 illustrate methods in a wireless device according to someembodiments.

Referring to FIG. 10, a method is provided in a wireless device forreporting channel state information, CSI, to a network node. This methodmay be implemented in the wireless network shown in FIG. 5.

The wireless device receives a CSI process configuration for one or moreCSI processes from the network node. Each CSI process corresponds to areference signal resource and an interference measurement resource. Thereference signal resource comprises a set of resource elements in whichone or more reference signals corresponding to a desired signal arereceived. “Desired signal” in this context means a signal intended forreception by the wireless device. The interference measurement resourcecomprises a set of resource elements in which one or more signalsassumed to be interfering with the desired signal are received. Inparticular embodiments the reference signal resource is a CSI-RSresource. However, the reference signal resource may be any other typeof RS resource which may be used to estimate a desired signal, e.g. aCRS resource.

The wireless device further receives a request for CSI information fromthe network node. The CSI request may e.g. be comprised in downlinkcontrol information (DCI) in the form of a flag, or it may be comprisedin a higher-layer message e.g. an RRC message. The CSI request may be arequest for an aperiodic, or a periodic CSI report.

The wireless device determines a maximum CSI processing time based e.g.on the number of configured CSI processes or the number of configuredCSI-RS resources. The maximum CSI processing time may also be referredto as an “allowed CSI processing time”. In a variant, the maximum CSIprocessing time is CSI-process-specific, i.e. each CSI process isassociated with a maximum CSI processing time.

The wireless device performs measurements based on one or more referencesignals received in the reference signal resource for each configuredCSI process, e.g. based on one or more CSI-RS. Depending on the CSIprocess configuration for the wireless device, some or all of thereference signal resources may be received in the same subframe. Inaddition, the wireless device estimates interference e.g. based onmeasurements on an IMR, as described above.

The wireless device then determines CSI information for each configuredCSI process, within the allowed CSI processing time. In the variantwhere each CSI process is associated with a maximum CSI processing time,the wireless device will determine CSI information for each configuredCSI process within the maximum processing time for that process. Thus,in this variant, the wireless device may start by determining CSIinformation for the processes that have the shortest maximum processingtime, to ensure that the timing restrictions can be met.

Finally, the wireless device transmits CSI to the network node. Such atransmission can be requested by the network in an aperiodic CSI request(scheduled in a DCI block) or it could be scheduled to occurperiodically in specific subframes.

FIG. 11 illustrates a similar embodiment, but in the method of FIG. 11the wireless device also determines a priority order for the configuredCSI processes, and determines CSI information for each CSI processaccording to the priority order. The prioritization may involveidentifying a causal relationship between certain CSI processes, whereinone or more CSI values from one process can be reused for anotherprocess, as was described above.

FIG. 12 is a further variant of the method in FIG. 11. Here, thewireless device also determines a priority order, and determines CSI forthe process with the highest priority within the maximum processing time(as shown in FIG. 8). In a variant, an indication of the priority ordermay be received from the network. For example, the wireless may receive,as part of the CSI process configuration, a priority indicator or indexfor each CSI process.

If the wireless device cannot determine CSIs for all CSI processeswithin the maximum processing time, the remaining CSI information willbe based on previous measurements.

It should be noted that the network node has performed the correspondingprioritization (and optionally communicated this prioritization of CSIprocesses to the wireless device) and therefore knows which CSIprocesses it should expect to be updated within the maximum processingtime, and which CSI processes are expected to be outdated.

FIG. 13 illustrates a method in a network node for CSI reporting.

The network node, e.g. an eNodeB, transmits, to a wireless device, e.g.an UE, a CSI process configuration for one or more CSI processes. EachCSI process corresponds to a reference signal resource and aninterference measurement resource. The reference signal resourcecomprises a set of resource elements in which one or more referencesignals corresponding to a desired signal are received. “Desired signal”in this context means a signal intended for reception by the wirelessdevice. The interference measurement resource comprises a set ofresource elements in which one or more signals assumed to be interferingwith the desired signal are received. In particular embodiments thereference signal resource is a CSI-RS resource. However, the referencesignal resource may be any other type of RS resource which may be usedto estimate a desired signal, e.g. a CRS resource.

The network node further transmits a request for CSI information to thewireless device. The CSI request may e.g. be comprised in downlinkcontrol information (DCI) in the form of a flag, or it may be comprisedin a higher-layer message e.g. an RRC message. The CSI request may be arequest for an aperiodic, or a periodic CSI report.

The network node further determines a maximum CSI processing time basede.g. on the number of configured CSI processes or the number ofconfigured CSI-RS resources. In a variant, the maximum CSI processingtime is CSI-process-specific, i.e. each CSI process is associated with amaximum CSI processing time.

Optionally, the network node also determines a priority order for theCSI processes. As described above, the priority order may be determinedbased on a causality relationship between CSI processes.

The network node receives CSI information corresponding to the CSIprocesses from the wireless device, within the maximum CSI processingtime. In the variant where a priority order is determined, the networknode may receive CSI information for some CSI processes (having a higherpriority) within the maximum processing time, and receive the remainingCSI information at a later point in time.

Optionally, the network node performs link adaptation and/or makes ascheduling decision based on the received CSI.

Referring to FIG. 16, according to some embodiments a method is providedin a wireless device for reporting channel state information, CSI. Thismethod may be implemented in the wireless device 540 shown in FIG. 5.The wireless device is comprised in a wireless network, e.g. wirelesscommunications system 500 of FIG. 5. In some variants, the wirelessdevice is a user equipment, UE.

The wireless device receives 1610 a CSI process configuration and arequest for CSI information from a network node 560. The request for CSIinformation may be a request for a periodic CSI report, or a request foran aperiodic CSI report. The wireless device then reports 1620 CSI forone or more CSI processes, wherein the CSI is determined such as toreflect the state of the channel for a CSI reference resource. The CSIreference resource is determined based on the number of configured CSIprocesses. Optionally, the CSI reference resource is also determinedbased on the number of configured CSI-RS resources.

The wireless device may determine CSI based on measurements performed onreference signal resources corresponding to the configured CSIprocesses. In a particular variant, the CSI is determined based onmeasurements performed in and/or prior to the CSI reference resource. Asdescribed above, determining the CSI may further comprise performingmeasurements on interference measurement resources corresponding to theconfigured CSI processes, and determine the CSI based on thesemeasurements.

In some variants, the wireless device determines a number nCQI_refrepresenting the location of the CSI reference resource relative to thesubframe in which the CSI report is transmitted. The wireless device maydetermine one number nCQI_ref which is applied to all CSI processesconfigured for the device. Alternatively, different numbers nCQI_ref maybe determined for different CSI processes. In some variants, the numbernCQI_ref increases when the number of configured CSI processes exceeds acertain threshold. In another variant, nCQI_ref increases with thenumber of configured CSI processes.

Optionally, the wireless device prioritizes a first CSI process over asecond CSI process, e.g. based on a CSI process index or identity. Thewireless device then determines a rank indicator and/or a precodingmatrix indicator for the first CSI process, and reuses the determinedrank indicator and/or precoding matrix indicator for the second CSIprocess.

Although the described solutions may be implemented in any appropriatetype of telecommunication system supporting any suitable communicationstandards and using any suitable components, particular embodiments ofthe described solutions may be implemented in an LTE network, such asthat illustrated in FIG. 5.

As shown in FIG. 5, the example network may include one or moreinstances of user equipment (UEs) and one or more base stations capableof communicating with these UEs, along with any additional elementssuitable to support communication between UEs or between a UE andanother communication device (such as a landline telephone). Althoughthe illustrated UEs may represent communication devices that include anysuitable combination of hardware and/or software, these UEs may, inparticular embodiments, represent devices such as the example UEillustrated in greater detail by FIG. 15. Similarly, although theillustrated base stations may represent network nodes that include anysuitable combination of hardware and/or software, these base stationsmay, in particular embodiments, represent devices such as the examplebase station illustrated in greater detail by FIG. 14.

With reference to FIG. 15, some embodiments provide a wireless device1500 for reporting Channel State Information, CSI. The wireless devicemay be a user equipment. The wireless device is adapted to receive a CSIprocess configuration and a request for CSI information from a networknode, and to report CSI for one or more CSI processes. The CSI isdetermined such as to reflect the state of the channel for a CSIreference resource, and the CSI reference resource is determined basedon the number of configured CSI processes.

Optionally, the wireless device is adapted to determine the CSIreference resource also based on the number of configured CSI-RSresources.

The wireless device may further be adapted to determine CSI based onmeasurements performed on reference signal resources corresponding tothe configured CSI processes. In a particular variant, the wirelessdevice is adapted to determine CSI based on measurements performed inand/or prior to the CSI reference resource. The wireless device may befurther adapted to determine the CSI by performing measurements oninterference measurement resources corresponding to the configured CSIprocesses, and determine the CSI based on these measurements.

In some variants, the wireless device is adapted to determine a numbernCQI_ref representing the location of the CSI reference resourcerelative to the subframe in which the CSI report is transmitted. Thewireless device may further be adapted to determine one number nCQI_refwhich is applied to all CSI processes configured for the device.Alternatively, the wireless device may be adapted to determine differentnumbers nCQI_ref for different CSI processes. In some variants, thewireless device is adapted to determine the number nCQI_ref such that itincreases when the number of configured CSI processes exceeds a certainthreshold. In another variant, the wireless device is adapted todetermine the number nCQI_ref such that it increases with the number ofconfigured CSI processes.

Optionally, the wireless device is adapted to prioritize a first CSIprocess over a second CSI process, e.g. based on a CSI process index oridentity. The wireless device is then further adapted to determine arank indicator and/or a precoding matrix indicator for the first CSIprocess, and to reuse the determined rank indicator and/or precodingmatrix indicator for the second CSI process.

Referring again to FIG. 15, some embodiments provide a user equipment1500 for reporting Channel State Information, CSI, the user equipment1500 comprising a processor 1520 and a memory 1530, the memory 1530comprising instructions executable by said processor whereby said userequipment 1500 is operative to receive a CSI process configuration and arequest for CSI information from a network node, and to report CSI forone or more CSI processes, wherein the CSI is determined such as toreflect the state of the channel for a CSI reference resource, and theCSI reference resource is determined based on the number of configuredCSI processes.

Optionally, the instructions, when executed, cause the user equipment1500 to be operative to determine the CSI reference resource also basedon the number of configured CSI-RS resources.

In some embodiments the instructions, when executed, cause the userequipment 1500 to be operative to determine CSI based on measurementsperformed on reference signal resources corresponding to the configuredCSI processes. In a particular variant, the wireless device is caused tobe operative to determine CSI based on measurements performed in and/orprior to the CSI reference resource. The wireless device may be furthercaused to be operative to determine the CSI by performing measurementson interference measurement resources corresponding to the configuredCSI processes, and determine the CSI based on these measurements.

In some variants, the instructions, when executed, cause the userequipment 1500 to be operative to determine a number nCQI_refrepresenting the location of the CSI reference resource relative to thesubframe in which the CSI report is transmitted. The wireless device mayfurther be caused to be operative to determine one number nCQI_ref whichis applied to all CSI processes configured for the device.Alternatively, the wireless device may be caused to be operative todetermine different numbers nCQI_ref for different CSI processes. Insome variants, the wireless device is caused to be operative todetermine the number nCQI_ref such that it increases when the number ofconfigured CSI processes exceeds a certain threshold. In anothervariant, the wireless device is caused to be operative to determine thenumber nCQI_ref such that it increases with the number of configured CSIprocesses.

Optionally the instructions, when executed, cause the user equipment1500 to be operative to prioritize a first CSI process over a second CSIprocess, e.g. based on a CSI process index or identity. The wirelessdevice is then further operative to determine a rank indicator and/or aprecoding matrix indicator for the first CSI process, and to reuse thedetermined rank indicator and/or precoding matrix indicator for thesecond CSI process.

As shown in FIG. 15, the example UE includes a processor, a memory, atransceiver, and an antenna. In particular embodiments, some or all ofthe functionality described above as being provided by mobilecommunication devices or other forms of UE may be provided by the UEprocessor executing instructions stored on a computer-readable medium,such as the memory shown in FIG. 15. Alternative embodiments of the UEmay include additional components beyond those shown in FIG. 15 that maybe responsible for providing certain aspects of the UE's functionality,including any of the functionality described above and/or anyfunctionality necessary to support the solution described above.

As shown in FIG. 14, the example base station includes a processor, amemory, a transceiver, and an antenna. In particular embodiments, someor all of the functionality described above as being provided by amobile base station, a base station controller, a node B, an enhancednode B, and/or any other type of mobile communications node may beprovided by the base station processor executing instructions stored ona computer-readable medium, such as the memory shown in FIG. 14.Alternative embodiments of the base station may include additionalcomponents responsible for providing additional functionality, includingany of the functionality identified above and/or any functionalitynecessary to support the solution described above.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”.

The present invention is not limited to the above-describe preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

1-16. (canceled)
 17. A method, in a wireless device, for reportingChannel State Information (CSI), the wireless device being comprised ina wireless communications system, the method comprising: receiving a CSIprocess configuration and a request for CSI information from a networknode; determining a CSI reference resource based on a number ofconfigured CSI processes; reporting CSI for one or more CSI processes,wherein the CSI is reflects a state of a channel for the CSI referenceresource.
 18. The method of claim 17, further comprising determining anumber N representing a location of the CSI reference resource relativeto a subframe in which the CSI report is transmitted.
 19. The method ofclaim 18, wherein N increases when the number of configured CSIprocesses exceeds a certain threshold.
 20. The method of claim 18,wherein N increases with the number of configured CSI processes.
 21. Themethod of claim 18, wherein N is applied to all CSI processes configuredfor the wireless device.
 22. The method of claim 17, wherein thedetermining the CSI reference resource comprises determining the CSIreference resource further based on a number of configured CSI-RSresources.
 23. The method of claim 17, further comprising: prioritizinga first CSI process over a second CSI process; determining a rankindicator and/or a precoding matrix indicator for the first CSI process;reusing the determined rank indicator and/or precoding matrix indicatorfor the second CSI process.
 24. The method of claim 17, furthercomprising: performing measurements on reference signal resourcescorresponding to the configured CSI processes; determining the CSI basedon the measurements.
 25. The method of claim 17, wherein the CSI isdetermined based on measurements performed in and/or prior to the CSIreference resource.
 26. The method of claim 17, wherein the request forCSI information is a request for a periodic CSI report, or a request foran aperiodic CSI report.
 27. The method of claim 17, further comprising:performing measurements on interference measurement resourcescorresponding to the configured CSI processes; determining the CSI basedon the measurements.
 28. A wireless device for reporting Channel StateInformation (CSI), the wireless device comprising: memory comprisinginstructions; processing circuitry operatively connected to the memoryand configured, when executing the instructions, to cause the wirelessdevice to: receive, from a network node, a CSI process configuration anda request for CSI information; determine a CSI reference resource basedon a number of configured CSI processes; report CSI for one or more CSIprocesses, wherein the CSI reflects a state of a channel for the CSIreference resource.
 29. The wireless device of claim 28, wherein thewireless device is a user equipment.
 30. The wireless device of claim28, wherein the processing circuitry is further configured to determinea number N representing a location of the CSI reference resourcerelative to a subframe in which the CSI report is transmitted.
 31. Thewireless device of claim 28, wherein the processing circuitry, whenexecuting the instructions, is further configured to determine the CSIreference resource further based on a number of configured CSI-RSresources.
 32. The wireless device of claim 28, wherein the processingcircuitry, when executing the instructions, is further configured to:prioritize a first CSI process over a second CSI process; determine arank indicator and/or a precoding matrix indicator for the first CSIprocess; reuse the determined rank indicator and/or precoding matrixindicator for the second CSI process.
 33. The wireless device of claim28, wherein the processing circuitry, when executing the instructions,is further configured to: perform measurements on reference signalresources corresponding to the configured CSI processes; determine theCSI based on the measurements.
 34. The wireless device of claim 28,wherein the processing circuitry, when executing the instructions, isfurther configured to determine the CSI based on measurements performedin and/or prior to the CSI reference resource.
 35. The wireless deviceof claim 28, wherein the processing circuitry, when executing theinstructions, is further configured to: perform measurements oninterference measurement resources corresponding to the configured CSIprocesses; determine the CSI based on the measurements.